This invention relates to testing electronic circuits and more particularly to the troubleshooting of electronic circuit boards to locate a failing component.
When an electronic circuit board does not perform properly, it is necessary for the technician first to locate the failing node in the circuitry and then to determine the failing component connected to that node. There are many techniques for locating the failing node. One common practice is to measure the voltage level at each node and compare it to standard levels to determine whether the voltage at that node is within limits. An oscilloscope may be used for this purpose in a similar manner.
After the failing node is located, the real problem is in determining which component connected to the node is defective or if there is a connection to some circuitry which is not supposed to be connected to the node. Commonly, the technician visually checks the circuitry for short circuits which may or may not be visible. If he finds none, the common practice is to replace the component driving the node. However, the assumption that it is this component which is failing is not always valid. Components having inputs connected to the node often fail in a manner which causes an erroneous voltage level to appear on the node.
In order to properly determine the failing component, the technician needs to know the cause of the logic levels being observed. More particularly, a determination must be made of the currents producing the voltage levels and the direction of those currents.